Laminated structures and methods and compositions for producing same

ABSTRACT

Methods for bonding two substrates, one of which is polymeric, which comprise coating the surface of at least one substrate with an adhesive composition comprising a major component which is an adhesive for the first substrate and a minor disperse phase which is a solution of a polymer in a solvent for the polymeric substrate and contacting the coated surface of the one substrate with the surface of the other substrate, together with adhesive compositions useful for joining such substrates, laminates so formed, and articles comprised of such laminates.

This is a continuation, division, of application Ser. No. 573,924 filedMay 2, 1975 now U.S. Pat. 3,988,521 which, in turn, is a continuation ofappln. Ser. No. 275,951, filed 7/28/72, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to methods for bonding substrates, such aspolymer sheets to provide laminates for use in fabricating articles suchas containers, and to novel laminates and adhesive compositions forlaminating such materials.

The use of adhesives for bonding various similar and dissimilarmaterials is old and well known. However, difficulties still arise whendissimilar materials are to be bonded or laminated to one another, andthese difficulties are frequently compounded when the laminates are tobe subjected to various factors inimical to the adhesive characteristicsof the materials.

One instance of such difficulties is illustrated by the laminatedmaterials sought for use in the large-scale production of disposablecontainers, such as those used for coffee, soups, and other hot liquids.It is desirable to produce such containers easily and at a minimum ofcost so they can be used by the consumer and discarded. It is furtherdesirable that the containers be strong as well as attractivelydecorated and capable of receiving printing, lithography and the like.

It has accordingly been sought to provide a laminate of paper andpolystyrene foam so that the paper can be decorated to provide anattractive appearance and the foam will provide impermeability to liquidcontents and low heat transfer, in order that a cup of hot liquid can becomfortably held by the consumer. The dissimilarity of the poroushydrophilic paper substrate and the polystyrene has created problems inobtaining adequate adhesion, and this problem is especially severe wbenthe laminates are to be contacted with hot liquids. In fact, up to thepresent time, no satisfactory, readily produced laminates, such as thoseof paper and polystyrene foam have been available to withstand hotliquids.

U.S. Pat. No. 3,378,424 shows the application of polymeric coatings tofibrous substrates. The process there shows treatment of the fibroussubstrate with an aqueous emulsion containing a wax and anethylene-vinyl acetate copolymer. No solvent for the polymeric coatingis involved.

U.S. Pat. No. 2,917,217 shows laminates of paper and polystyrene foam,and the adhesive recommended for use in a synthetic resin having apolyvinyl acetate base.

U.S. Pat. No. 2,510,908 shows an adhesive comprising polystyrene,toluene, and a triaryl phosphate plasticizer for bonding polystyrene topaper and other surfaces. The adhesive bonds are not exposed to aqueousor high-temperature environments. U.S. Pat. No. 3,112,235 shows anadhesive method utilizing borates and polyvinyl alcohol.

U.S. Pat. No. 2,628,180 shows an adhesive using styrene monomer,solvent, and an alkoxyethyl stearate evaporation retarder, while U.S.Pat. No. 2,975,093 relates to a process for laminating cellulosic sheetswith one another by treating the surfaces of the sheets with polyvinylalcohol solutions. Various other adhesive compositions and methods areshown in U.S. Pat. Nos. 3,135,648 and 2,434,106.

THE INVENTION

Briefly, the presently described invention provides methods andadhesives for bonding or laminating a first substrate to a high polymersubstrate so that the combination is highly resistant to hot aqueousenvironments. The process comprises applying to the surface of at leastone of the substrates a novel adhesive composition and then contactingthe adhesive coated substrate and the other substrate to form a stronglybonded structure. The adhesive composition comprises a major componentand a minor disperse phase wherein the major component is an adhesivefor the first substrate and the minor disperse phase is a polymerdissolved in a solvent for the high polymer substrate. The presentinvention also contemplates laminates so obtained and articles, such asfoodstuff containers and the like, prepared from such laminates.

The invention is hereinafter further depicted with reference to theaccompanying drawings, wherein

FIG. 1 is a sectional view of a container prepared with laminatesaccording to the invention, and

FIG. 2 is an enlarged section through A--A of FIG. 1.

The presently described process can be used to provide a strong,temperature-resistant adhesive bond to a wide variety of dissimilarmaterials. One substrate should be soluble to some significant extent ina solvent, and this solvent should be dispersed as a minor phase in anadhesive bond for the other substrate. Thus, for example, polystyrenecan be adhesively bonded to polyvinyl chloride, a polyester, a urethane,or the like.

The invention is herein chiefly described in terms of bonding a singlesheet of porous material such as paper to a single sheet of highpolymeric material such as polystyrene. It will be understood however bythose skilled in the art after reading the present disclosure that anynumber of layers of high polymer sheets can be so laminated to othermaterials and that a wide variety of useful articles can thereby beproduced.

The term "first substrate" will be used herein to means one the surfaceof which can be attacked or penetrated by a liquid adhesive so that agood bond is thereby formed. The solid first substrate can assume a widevariety of physical dimensions, but the present invention is very welladapted to hydrophilic materials such as paper or other nonwoven webscomprising cellulosic fibers such as paper, rayon staples, and the like.The present description is accordingly stated chiefly in terms oflaminating high polymer materials to substrates of cellulosic materials.

The term high polymer is used herein to describe the polymeric materialwhich is bonded or laminated to the first substrate. It distinguishesthe solid material to be bonded from the hereinafter described polymerwhich is used in the adhesive composition. The high polymer material isa solid which can be dissolved at least to some extent in a solvent. Itis desirably a material such as polystyrene, acrylic, methacrylic, andlike high polymers, which can form a fairly rigid structure. Aparticularly preferred high polymer material herein is polystyrene.

The adhesive composition is coated on or applied to the surface of atleast one of the substrates. Coating is herein taken to mean coveringthe entire surface or substantially the entire surface of the substrateto be bonded with the adhesive composition. For special uses or where itis desirable that only part of the surfaces be bonded to one another,the adhesive composition can be printed, stamped, or otherwise depositedon the substrate surface in a desired pattern. The coating itself iscarried out by conventional means such as doctor blades, wire-woundrods, roller mills, gravure rolls, and like devices.

The adhesive composition can be coated on a surface of each of the twosubstrates to be bonded. Desirably, in certain embodiments of theinvention the adhesive composition is coated onto one of the surfaces,and then the composition-coated surface is contacted with the othersubstrate. The coating compositions are desirably coated onto thesubstrate surfaces in thicknesses of from about 0.2 mils (thousandths ofan inch) to about 3 mils. In certain preferred embodiments of theinvention, the adhesive composition is coated onto the high polymersubstrate since the minor phase can then begin bond formation. Thecoating can be carried out in one step or a plurality of steps. Incertain preferred embodiments, excellent control of adhesive thicknessis obtained by using a wire-wound rod. The thickness is controlled bythe diameter of wire wound on the rod.

If desired, after coating the substrate can be permitted to stand for aperiod of time so that the adhesive composition can form an initial set.In the usual embodiments of this process, the second substrate iscontacted with the adhesive coated surface of the first substrateimmediately after coating. The contacting is desirably carried out witha roller set or other means to ensure good contact and to express anyair bubbles which might be included between the substrates.

Initial bonding of the substrates using the present method is very good,and the ultimate bond strength is reached in a few hours. There will ofcourse be individual variations in bonding time depending upon theparticular substrates, used, elevated drying temperatures if used, theadhesive components, ambient conditions, and the like. As an instance ofbond formation attained by the present invention, a laminate preparedfrom paper and polystyrene foam will tear in the fibers of the papersubstrate when it is sought to separate the substrates. Separation doesnot occur at or within the adhesive interface.

In preferred embodiments of the invention wherein paper is bonded topolystyrene, the paper desirably has a thickness of from about 3 toabout 20 mils, and thicknesses of 5 to 15 mils are generally preferred.Thus, paper having a weight of 107 lb/ream (about 10.5 lb/ft³ and 10.5mil caliper) and of 115 lb/ream (10.7 mil caliper) have given excellentresults.

The high polymer should have sufficient thickness to contribute thedesired physical properties to the finished article. It is generallyutilized in the form of sheets which can be solid or of an expandedstructure commonly known as foam. When a foam material is utilized, itsthickness and density can be selected to provide any desired insulatingproperties. On the other hand, excessive thicknesses (and/or density)wastes material and provides no substantial benefits. It is accordinglydesirable that the high polymer sheet thickness be from about 5 to about50 mils and the foam density be from about 4 to about 25 lb/ft³, andthicknesses of 5 to 25 mils and densities of 5 to 20 lb/ft³ arepreferred.

The high polymer substrate can be selected from a wide variety ofmaterials. The high polymer can be a homopolymer such as polystyrene orit can be a modified polymer or copolymer such as rubber-modifiedpolystyrene. Such rubber-modified polystyrenes are also known as medium-or high-impact polystyrenes, depending upon the quantity and type ofmodifier used.

When the high polymer substrate comprises polystyrene, the polymergenerally has average molecular weights on the order of 50,000 up toabout 400,000. The preferred commercial styrene substrates havemolecular weights of from about 120,000 to about 200,000.

The adhesive composition itself is comprised largely of an adhesive forthe first substrate. This major component serves to hold the minor phasein suspension. A relatively large quantity of this component is alsoparticularly required with porous substrates because such substratestend to absorb it. Accordingly, the major component desirably comprisesfrom 65 percent to 95 percent or more of the composition, and inpreferred embodiments, it comprises 80 to 90 percent of the totalcomposition. All parts, percentages, proportions and ratios herein areby weight unless otherwise indicated.

The major component of the adhesive composition is comprised of amaterial which is a conventional adhesive for the first substrate. Themajor component can either be a continuous phase or can itself comprisea plurality of phases. For example, it can be a plasticizer for thefirst substrate, a plastisol, an organosol, or a latex. The particulartype of adhesive utilized as the major component chiefly depends uponthe nature of the first substrate, as will be appreciated from thepresent description by those skilled in the art. The major componentmust of course not be destructive of, or otherwise damaging to, the highpolymer substrate.

Thus, when the first substrate is cellulosic, aqueous latices have beenfound to provide excellent results as the major component. Such laticesare themselves emulsions or such dispersions of small particles of anorganic material in a continuous phase of water. Excellent results withcellulosic first substrates have been obtained by using a major adhesivecomponent which is an aqueous emulsion of long-chain hydrocarbonbackbones which are randomly and irregularly substituted with sidechains having a chain length of not more than about three atoms.

More desirably, the major component comprises copolymers of ethylenewith terminally ethylenically unsaturated organic compounds containingfrom three to five carbon atoms. Such comonomers are alpha-olefins,esters of terminally ethylenically unsaturated monocarboxylic acids andunsaturated aliphatic alcohols, or esters of saturated monocarboxylicacid and terminally ethylenically unsaturated aliphatic alcohols.Examples of such comonomers are unsaturated esters such as vinylacetate, ethyl or methyl acrylate, and normal lower alpha-olefins suchas propylene, butene-1, and pentene-1.

In certain preferred embodiments with cellulosic first substrates andpolystyrene polymer substrates, a major component comprising an aqueousemulsion of acetoxylated ethylene-vinyl acetate copolymer has givenexcellent results. Such major components should have a solids contentwhich is sufficient to form a good bond with the cellulosic substratebut not so much as to create such a high viscosity that the fluidcomposition does not spread readily on the substrates. The copolymercontent of the major component is generally adjusted to provideviscosities in the area of from about 200 to 1200 cp, with preferredviscosities being from about 600 to 700 cp. With the ethylene-vinylacetate copolymers discussed above, preferred solids contents in theaqueous major component range from about 35 percent to about 60 percent.

The minor phase is dispersed throughout the major component. The minorphase contains a dissolved or solute polymer is a solvent which will atleast partially dissolve the high polymer substrate. It will beunderstood that the polymer dissolved in the minor phase need not be thesame as that of the high polymer substrate, although the polymer shouldbe compatible with and capable of adhering to the high polymersubstrate.

It is desirable in certain aspects hereof that the polymer be the samechemically as the high polymer forming the substrate. For example, ifthe substrate is polystyrene then the solute polymer is desirably alsopolystyrene. In fact, it has been found advantageous that the solutepolymer be the same chemically as the high polymer substrate and that ithave a molecular weight sufficient to remain substantially unmelted atthe temperatures of the liquids to which the bonded substrates areexposed. On the other hand, use of excessively high molecular weightsolute polymers makes the minor phase viscous and difficult to dispersein the major component. Based on these considerations, it is desirablethat the solute polystyrene polymer have an average molecular weight offrom about four to about 100 percent of the high polymer, and it ispreferred that the average molecular weight of polystyrene solutepolymers be from about five percent to about 15 percent of the averagemolecular weight of the polystyrene in the substrate. This providesgreater solubility of the solute polymer in the solvent and facilitatesformation of a bond between the solute polymer and the substratepolymer.

The solvent in the adhesive composition is one which will at leastslightly attack or etch the surface of the high polymer substrate andpermit the formation of a bond with the components of the minor phase.The solvent can be chosen by one skilled in the art from theconsiderations stated herein. By way of illustration, when the highpolymer substrate is polystyrene foam, the solute can be polystyrene,and the solvent can be a liquid solvent for the polystyrene solute andthe polystyrene substrate. Such solvents are materials in which soluteand polymer substrates have appreciable solubility. In the case ofpolystyrene, these include such art-recognized liquids as aromatic andsubstituted aromatic hydrocarbons like benzene, toluene, xylene,styrene, vinyl toluene, and the like, halogenated hydrocarbons andparticularly chlorinated and brominated hydrocarbons such as methylchloride, methylene chloride, chloroform, carbon tetrachloride,trichloroethylene, tirchloroethane, methyl bromide, ethyl bromide,propyl bromide, bromoform, tribromoethane, and the like, aliphaticesters such as ethyl acetate, butyl acetate, propyl formate, and thelike, methyl, ethyl and butyl phthalate, aliphatic and alicyclic ketonesand aldehydes such as methyl ethyl ketone, cyclohexanone, and the like,aliphatic and cyclic ethers such as dibutyl ether, dioxane,tetrahydrofuran, tetrahydrofurfuryl alcohol, glycol formal, diethyleneglycol dibutyl ether, propylene oxide, and the like, aliphatic alcoholssuch as ethylhexanol and the like, organic phosphorus compounds such astributyl phosphate and the like, organic sulfur compounds such as carbondisulfide, ethyl mercaptan, and the like.

It will further be understood that combinations of two or more suchmaterials or combinations such as acetonecyclohexane and the like canalso be utilized. Some of the solvent systems are preferred for certainapplications, depending on the toxicity hazard, economic considerations,the particular material to be used in conjunction with the polystyrenepolymeric substrate and so on.

The quantity of solvent used in the composition will be the balance leftafter the quantity of major component, the quantity of solute polymer,and the quantity of any additional adjuvants are determined in thecomposition. The quantity of solvent for the solute polymer should besufficient to dissolve the solute polymer and to etch the surface of thehigh polymer substrate so that the solute polymer particles will adhereor "anchor" to the high polymer substrate. There is also preferablysufficient solvent so that the evaporation which may occur prior toapplication will not adversely affect the properties of the adhesivecomposition. Too much solvent, based on the total composition, willadversely affect the viscosity thereof.

The quantity of solvent to be used is also determined, at least in part,by the nature of the high polymer substrate. Less solvent is requiredwith a coarse-celled foam because the surface cell walls collapse andare easily etched, whereas a dense or fine-celled foam or a solid highpolymer generally requires more solvent sufficiently to etch the surfaceto provide anchor sites. The quantity of solvent is accordingly fromabout three to about 25 percent of the adhesive composition. In certainpreferred embodiments the quantity of solvent is from about 8 percent toabout 20 percent of the adhesive composition.

The quantity of solute polymer in the solvent is sufficient to bond withthe high polymer substrate at a number of sites sufficient to form agood juncture. In practice it has been found that a quantity of solutepolymer to comprise from about 15 to about 50 percent of the minor phaseis desirable, and amounts of from about 25 to 35 percent of the solventare preferred. Accordingly, the solute polymer will generally comprisefrom about two percent to about ten percent of the total adhesivecomposition.

The solvent-solute polymer component must be dispersed substantiallyuniformly throughout the major component of the adhesive composition.This can be accomplished by the use of a mix tank and vigorous mixing orby high-shear or high-rate mixing devices such as a blendor, aDispersator and the like. The size of the particles of the minor phasepreferably lie in the range of 50 to 125 microns in effective diameter.If the particles are too small a good bond of the hig polymer substrateis not obtained, and when the size is too large, the particles may notbond evenly and may also tend to agglomerate and separate from the majorphase. Particle sizes of 75 microns have been found to give good resultswith the polystyrene adhesive compositions of the present invention.

Either the minor phase or the major component of the adhesivecomposition, or both phases, can contain adjuvant materials to alter,vary, modify or improve, hereinafter simply "alter", the properties ofthe composition, the laminate or the finished articles. Thus,plasticizers, dyes, anti-microbial agents and other preservatives,whiteners, pigments, insolubilizers, solubilizers, viscosity controlagents, other polymers, and like materials can be present in theadhesive composition in amounts which do not essentially affect suchcompositions. By way of illustration, it has been found desirable incertain embodiments to incorporate an insolubilizing agent such as aWerner-type aliphatic acylato chromic complex into the major phase toremove hydroxyethyl cellulose employed in certain commercially availableethylene-vinyl acetate copolymers as a protective colloid. When theadhesive compositions of this invention are to be used significantlyafter preparation, it is desirable to utilize preservatives known in theart to protect the composition against oxidation, microbial attack, andthe like. The adhesive composition can also contain plasticizers andother such adjuvants to alter the flexibility and temperature-resistanceof the adhesively bonded laminate. Additional plasticisers also improvethe initial tack or bond formation in some embodiments.

The laminates produced with the adhesive compositions and according tothe processes of the present invention are found to have excellentresistance to delamination when in contact with hot, and even boiling,aqueous liquids. Microscopic examination of cross-sections of thelaminates shows that particles of the solute polymer are bonded to thesurface of the high polymer, and that the particles are, in turn,surrounded by the adhesive of the major component. It is inferred fromthese studies that the solute polymer is tighly bonded to the highpolymer substrate and that the solute polymer is mechanically lockedinto the major component adhesive. This accounts for the excellentdelamination resistance of the laminates of the present invention. It isbelieved that the relatively large solute polymer particles fuse to thehigh polymer substrate to form anchor sites and that the fused particlesare in turn surrounded by smaller particles (perhaps of large molecularsize or colloidal size) of the solids contained in the major component.In such a case the solids of the major component can actually interlockbehind or under the solute polymer particles and form a mechanical bondof sorts. The foregoing is inferred on the basis of available evidenceand is believed to account for the excellent high-temperature resistanceof the laminates, although the present invention provides excellentresults whatever the theoretical explanation of its action may be.

Indeed, adhesive compositions for cellulosic substrates and polystyrenesas described herein could be considered to comprise a three-phasesystem. The water of the aqueous major component would be considered thecontinuous phase, the solids of the major component could be consideredto be one disperse phase, and the minor solvent-solute phase would be asecond disperse phase present in lesser amount generally than either ofthe two other phases.

It is believed that the ratio of sizes of the particles in the majorcomponent to the solute-solvent particles of the minor phase should beat least 1:3 and preferably 1:10. In the aqueous systems taught hereinfor use with cellulosic substrates and polystyrene substrates, thesolute-solvent minor phase particle size is about 75 microns, while theethylene-vinyl acetate copolymers are about 0.3 microns in diameter.

The laminates of the present invention comprise at least one poroussubstrate adhesively bonded to at least one high polymer substrate by alayer which comprises an adhesive for the porous substrate in whichadhesive is dispersed a minor quantity of solute polymer particles. Aquantity of these solute polymer particles are fused to the high polymersubstrate and thus anchor the adhesive layer to such substrates. Thus,in the illustrative case of paper bonded to polystyrene foam, thelaminate comprises a paper sheet, an ethylene-vinyl acetate copolymerhaving dispersed therein particles of polystyrene, and the polystyrenefoam substrate. The thicknesses of the substrates are as set forthherein.

Such laminates are particularly suited to the production of receptaclesor continers for solid and liquid materials such as beverages, soups,yogurt, cottage cheese, salads, dips, and other foodstuffs. FIG. 1 showscup 10 designed for use in serving hot coffee, hot cocoa, hot tea andother such beverages. Also shown is cover or cap 11 made of the samelaminate.

The container can be formed by using a mandrel to impart afrusto-conical shape to a laminate blank prepared according to thepresent invention and then gluing the overlapping portion at seam 13.The container is provided with bottom member 14 crimped in place bytapered sidewall 12. The embodiment shown utilizes a bottom member ofthe same material as sidewall 12, but it will be understood that adifferent material such as coated paper, sheet styrene, other plastic,other composite, or the like can be used.

In FIG. 1, cup 10 is provided with a beaded mouth rim 15 to providestrength and a rounded edge at the top of the receptacle. Further, therim 15 provides an interlocking bead for ready attachment of cover 11 tocup 10. While in the embodiment shown in FIG. 1, cover 11 is constructedof the same material as sidewall 12, an all-plastic, paper, or othercomposite cover could be used. It will also be noted by those skilled inthe art from FIG. 1, that a cup 10 is nestable with similar cups byvirtue of its frustoconical form, so that a quantity of such cups can bestored in and dispensed from a space-conserving configuration.

FIG. 2 is a greatly enlarged section through A-A of FIG. 1. It showsouter porous substrate 20 joined to high polymer substrate 21 byadhesive layer 22 containing particles of solute polymer (not actuallyshown because of their diminutive size). In the embodiment shown, itwill be noted that the high polymer substrate 21 forms the interior ofcup 10 and porous substrate 20 forms the exterior. In this manner adesign can be printed on the substrate 20, while substrate 21 protectsit from direct contact with the contents of the cup. Moreover, whereporous substrate 20 is a material such as paper, it can contribute tothe overall strength and is a structural element of cup 10. It acts insuch instances to reinforce high polymer substrate 21.

In another form of constructing articles according to the presentinvention, a pre-formed high polymer container can be inserted into apaper or other overwrap or outer covering held in a mold. The exteriorof the pre-formed high polymer member can be coated with an adhesivecomposition according to the invention prior to insertion into theoverwrap.

The seams of the outerwrap where a pre-formed liner is used or seam 13in FIG. 1 can be secured by the adhesive compositions disclosed herein.A variety of adhesive compositions can be utilized to bond the seam, butit is desirable to utilize and adhesive compositions of the presentinvention, especially in embodiments in which the container isfabricated from laminates as shown in FIG. 1.

It will thus be understood from the present description that containersaccording to the present invention comprise sidewall and bottomportions, the sidewall portion 12 extending upwardly from the bottomportion 14 to an upper end providing an open mouth rim 15 for thecontainer. At least the sidewall portion is formed from a laminatecomprising a layer of a first material 20 secured to a high polymermaterial 21 by an adhesive for the first material, said adhesivecontaining polymer particles fused to the high polymer material. Thehigh polymer material, as taught herein, can either be a foam or a solid(unfoamed) high polymer.

The following examples are given to illustrate embodiments of theinvention as it is presently preferred to practice it. It will beunderstood that these examples are illustrative, and the invention isnot to be considered as restricted thereto except as indicated in theappended claims.

EXAMPLE I

Four pounds of polystyrene pellets is slowly added to 8 lb. of toluenewith constant agitation, the polystyrene having a molecular weight of18000-24000. Stirring is continued until all of the polystyrene isdissolved in the toluene solvent, and a mixture of 2 lb. of "Santicizer160" plasticizer (made by Monsanto Company, St. Louis, Mo., U.S.A.) and2 lb. of dibutyl phthalate is admixed with the polystyrene-toluenesolution.

The plasticizer-containing solution so obtained is then slowly added to80 lb. of "Aircoflex 510" acetoxylated ethylene-vinyl acetate copolymer(made by Airco Chemical Co., New York, New York, U.S.A) with continuousvigorous agitation and the vigorous agitation is continued for tenminutes after the addition of the polystyrene solution to provide adispersion of particles having approximately a 75-micron diameter in theaqueous copolymer. A vortex is maintained during polystyrene solutionaddition to ensure good dispersion of the solution. The copolymer alsocontains 2 lb. of Santicizer 160 and 2 lb. of dibutyl phthalate addedwith stirring prior to dispersion of the polystyrene solution to providethe final adhesive composition.

Blanks of polystyrene foam sheet having a density of 11 lb/ft³, amolecular weight of about 250,000 and a caliper (thickness) of 13 milsand measuring 12 by 5 inches are coated with the adhesive compositionusing a No. 12 Mayer rod. Paper of the same dimensions and having acaliper of 10.7 mils and a density of 11.5 lb/ft³ is layered over theadhesive-coated polystyrene foam sheet and then rolled to smooth out andeliminate air pockets. After lamination the foam-paper combination isdried for three to four hours at room temperature (about 70° F). Thepaper and foam are firmly bonded.

EXAMPLE II

An adhesive composition is prepared as in Example I by dissolving 5 lb.of the same polystyrene in 10 lb. of toluene solvent and then dispersingthe solution in 85 lb. of the same aqueous acetoxylated ethylene-vinylacetate copolymer. No plasticizer is used in this composition.

The composition is then coated on a sample of polystyrene foam as inExample I, and a layer of paper is similarly applied to the adhesivecomposition coating. After four hours of drying, the paper is found tobe firmly bonded to the foam.

EXAMPLE III

An adhesive composition is prepared according to the procedure ofExample II utilizing 5 lb. of polystyrene having a molecular weight of25,000 in lieu of the 18000-24000 molecular weight material. Used tolaminate paper to polystyrene foam as in Example II, the adhesivecomposition produces an excellent bond.

EXAMPLE IV

The procedure of Example III is repeated using 3 lb. of polystyrene inlieu of 5 lb. The results are substantially the same, an excellent bondbeing obtained.

EXAMPLE V

The procedure of Example I is repeated utilizing 8 lb. of Santicizer 160plasticizer instead of the 4 lb. of Santicizer 160 and 4 lb. of dibutylphthalate. Half of the plasticizer is added to the polystyrene solutionand half to the aqueous copolymer. A good bond of paper to foam isobtained.

EXAMPLE VI

The method of Example I is repeated utilizing 4 lb. of the polystyrenepellets, 4 lb. of toluene solvent, 6 lb. of Santicizer plasticizer, 5lb. of dibutyl phthalate, and 81 lb. of the aqueous copolymer to preparethe adhesive composition. A good bond is obtained between the foam andpaper with this composition.

EXAMPLE VII

The process of Example I is repeated utilizing 2 lb. of polystyrenepellets having a molecular weight of 250,000 and 1 lb. of polystyrenehaving a molecular weight of 600, 8 lb. of toluene solvent, 3 lb. ofdibutyl phthalate plasticizer, and 84 lb. of the aqueous copolymer. Agood paper-to-foam bond is obtained.

EXAMPLE VIII

The procedure of Example I is repeated using 2 lb. of polystyrenepellets having a molecular weight of 250,000, 8 lb. of toluene solvent,6 lb. of Santicizer 160 and 3 lb. of dibutyl phthalate plasticizer, and83 lb. of the aqueous copolymer to prepare the adhesive composition. Agood foam-to-paper bond is obtained.

For purposes of comparision, additional compositions are prepared withthe following ingredients:

Sample A -- 100 parts of Aircoflex 510 aqueous copolymer

Sample B -- 83 parts of Aircoflex 510, 5 lb. of Santicizer 160, 6 lb. ofdibutyl phthalate, and 6 lb. of polystyrene having a molecular weight of600

Sample C -- Same as B except polystyrene having a molecular weight of900 is used.

Sample D -- 90 parts of Aircoflex 510 containing 10 parts of toluenedispersed therein.

Composition Samples A through D are used to bond paper to foam as inExample I.

The laminated foam and paper strips are evaluated for laminationstrength by holding the specimen lengthwise vertically at roomtemperature with the paper surface facing the inspector. The inspectormakes a vertical downward initial tear and then tears the strip in thelongitudinal direction. The tear is then evaluated for adhesive failureand cohesive failure.

Separation in the adhesive is regarded as cohesive failure. Separationof the paper and foam without visible sign of either fiber tear in thepaper or foam face degradation is regarded as adhesive failure.

Hot water resistance of the laminate is evaluated by cutting samplesthereof into strips having dimensions of 8 by 1 inches. In order toavoid water directly reaching the paper component and to stiffen thespecimen, a water-resistant tape (Type 410 305L manufactured by 3M, St.Paul, Minnesota, U.S.A.) is layered over the paper side of the laminate.

The specimen strips are then immersed in boiling water for one minuteand evaluated. In boiling water the foam layer has a tendency to shrinkand pull away from the paper so that it curls and causes delamination.An adhesive which holds the foam to the paper under these severeconditions is rated "good". If severe or complete delamination occurs,the laminate is rated as a "failure". Intermediate or superiorperformances are rated accordingly.

The results of evaluating products of the preceding Examples and Samplesare set forth in Table I.

                  TABLE I                                                         ______________________________________                                                       Lamination  Hot Water                                          Specimen       Strength    Resistance                                         ______________________________________                                        Sample A       Fair        Failure                                            Sample B       Poor        Failure                                            Sample C       Poor        Failure                                            Sample D       Good        Failure                                            Example I      Excellent   Fair-to-Good                                       Example II     Excellent   Good                                               Example III    Excellent   Good                                               Example IV     Excellent   Good                                               Example V      Good        Fair                                               Example VI     Good        Poor-to-Fair                                       Example VII    Good        Good                                               Example VIII   Good        Fair-to-Good                                       ______________________________________                                    

It can be seen from the foregoing that there is some variation amonglaminates prepared according to the present invention, and that certainpreferred embodiments give superior results. By contrast, Sample A-Dmaterials all fail in hot water regardless of their original properties.

EXAMPLE IX

A mix tank equipped with a Cowles dissolver is charged with 74.6 partsof aqueous vinyl acetate-acetoxylated ethylene copolmer. A solution of2.6 parts of approximately 20,000 molecular weight polystyrene in 14parts of trichloroethylene is added to the mix tank while stirring thecontents thereof with the dissolver. After addition of the polystyrenesolution is completed, the stirring is continued for an additional tenminutes.

Sufficient water is then added to adjust the viscosity to 670-700 cp,and 4.4 parts of a 20% Quilon C Werner-type stearato chromic chloridecomplex (manufactured by E. I. Dupont, Wilmington, Delaware, U.S.A.) isadded to insolubilize the hydroxyethyl cellulose present as a protectivecolloid in the copolymer. This chloride complex improves the hot waterresistance of the copolymer. Sufficient water is then added to adjustthe final viscosity of the adhesive composition to 650-700 cp for use inapplication to the foam.

The adhesive composition so prepared is used in fabrication of a widevariety of laminates using polystyrene foams having densities from about4 lb/ft³ to 25 lb/ft³ and thicknesses from 5 to 25 mils. These laminatesare made with papers of a variety of weights from 8 to 20 lb/ft³ andthicknesses from 3 to 20 mils.

The laminates are used to prepare a variety of containers such as coffeecups, tubs for hot soups, chili, and the like, tops for containers, talltumblers, and the like. The containers are formed by methodsconventionally used for preparation of these articles. In some instancesthe paper is brightly printed so that the finished articles have a veryattractive appearance. These containers all have excellent resistance tohot liquids and exhibit good lamination strength.

It will be understood by those skilled in the art the presentdescription that arcylic and other foamed and non-foamed plastics can besimilarly laminated to paper, paperboard, cotton, and other cellulosicor absorbent materials by using suitable polymers, solvents, anddissolved lower polymers. Thus, polyvinyl acetate will bond acrylicplastics to paper with a disperse phase of an acrylic polymer dissolvedin an aromatic hydrocarbon. Butadiene-styrene latices are also useful insuch systems.

EXAMPLE X

A mix tank equipped with a Cowles dissolver is charged with 81.8 lb. ofehtylene-polyvinyl acetate copolymer and a solution of 2.9 lb. ofpolystyrene (having an average molecular weight of 25,000) in 15.3 lb.of trichloroethylene is added with stirring to maintain a good vortex inthe tank. After the polystyrene solution addition is completed, stirringis continued for an additional ten minutes to prepare the adhesivecomposition.

The adhesive composition is then used to laminate a 10 mil polystyrenesheet to 5 mil paper stock. The paper and polystyrene foam stock arecontinuously drawn from supply rolls at constant tension maintained byconventional means. The polystyrene web passes over a steel roll whereadhesive composition according to the present invention is spread on theweb. About two inches further past the steel applicator roll, the webpasses over a wire-wound Mayer rod which assures an even, controlledthickness of the adhesive composition. After traveling some eight feetfurther, the adhesive-coated polystyrene foam web is passed through thenip of a two-roll mill where it contacts the paper web on the coatedside of the foam. The laminate is then slit and rewound onto a takeuproll.

Laminate removed from the roll is found to have excellent adhesionbetween the paper and the foam. Containers prepared from the laminateare found to have excellent resistance to hot coffee, hot tea, boilingwater, and hot vegetable soup.

What is claimed is:
 1. A laminated structure comprising: (1) a substrateof high polymeric material, (2) a substrate of a porous hydrophiliccellulosic material, and (3) a layer bonding said substrates comprisingparticles of a polymer of the same kind as said high polymeric materialsubstrate (1) but of an average molecular weight of from about four toabout 100 percent of said high polymeric material substrate bonded tothe surface of said substrate (1) and a predominant amount of awater-dispersible adhesive preferentially adherent to said cellulosicsubstrate surrounding said bonded particles so as to mechanicallyinterlock with said particles.
 2. A laminate as defined in claim 1wherein said polymeric substrate is a styrene, acrylic or methacylicpolymer, and said porous hydrophilic cellulosic substrate is paper,rayon or paperboard.
 3. A laminate as defined in claim 1 wherein saidpolymeric substrate is foamed polystyrene.
 4. A laminate as defined inclaim 1 wherein said polymeric substrate (1) is polystyrene, said poroushydrophilic cellulosic material is paper, said adhesive polymer ispolystyrene, and said water-dispersible adhesive is a copolymer ofethylene and vinyl acetate.
 5. A laminate as defined in claim 4 whereinsaid polystyrene adhesive has an average molecular weight of from about5 to 15 percent of the average molecular weight of the polystyrenesubstrate and said water-dispersible adhesive is an acetoxylatedethylene-vinyl acetate copolymer.